Clickjacking is a web-based security vulnerability that tricks users into clicking on something different from what they perceive, potentially leading to unintended actions. It typically involves overlaying transparent or misleading elements over legitimate content, causing users to unknowingly interact with malicious sites or features. This can compromise user accounts, steal sensitive information, or execute harmful commands without the user's consent. Protections against clickjacking include frame busting techniques and the use of the X-Frame-Options HTTP header.